Integrated circuits are formed on wafers by well-known processes and materials. These processes typically include supplying a gas stream containing one or more gases to a semiconductor processing apparatus. Exemplary gases comprise reactant gases, carrier gases, diluent gases, and purge gases. Except for purge gas, a gas stream supplied to a semiconductor processing apparatus often includes two or more reactant gases and one or more carrier and diluent gases. In some applications, however, when one or more reactant gases should not be combined outside of a reaction chamber, two or more separate streams having different compositions are sent to the semiconductor processing apparatus. There is, therefore, a need for a flexible gas manifold for delivering two or more gas streams having different compositions and gas flow rates to a semiconductor processing system. Similarly, there is a need for delivering a gas stream having a first composition and flow rate, followed by a gas stream having a different composition and flow rate using the same gas delivery system.
Over the years, multistation semiconductor processing systems have been designed; that is, semiconductor processing systems that include a plurality of semiconductor processing stations or processing chambers. Therefore, there is a need for a gas delivery system that can provide a plurality of gas streams having a first composition and flow rate uniformly to a corresponding plurality of processing stations, and thereafter provide a plurality of different gas streams having a different composition and flow rate with the same uniformity to the processing stations.
In some semiconductor processing systems and processes, the plurality of processing stations are utilized at least sometimes under processing conditions that differ from one station to another. In some of these systems and processes, a semiconductor wafer is passed within a multistation system from one station to another, and different processes are performed at different stations. In such applications, it is common for a processing gas (a single gas or a gas mixture) supplied to one station to be different from the processing gas supplied to one or more other stations. For example, the total gas flow rate and gas mixture composition of a gas stream supplied to one semiconductor processing station may be different in one or more aspects from the gas flow rate and composition of gas streams supplied to other stations of the multistation system. In some of these multistation systems, two or more wafer processing stations are located in the same reaction chamber, but gas streams supplied to the individual wafer processing stations are not identical. In some of the multistation systems, one or more wafers are processed in each of several processing chambers that are located in a single apparatus or processing tool or system, and gas streams having different compositions are sent to the different chambers, or to different processing stations within a particular chamber. In some applications, therefore, it would be useful if a gas manifold could be used to provide gas streams having different flow rates and compositions to a plurality of semiconductor processing apparatuses. Since the same substrate processing apparatus is sometimes used for different phases of substrate processing, and since a particular processing apparatus is typically used under completely different process conditions for different types of substrates, there is a need for a gas delivery system that is flexible enough to provide a plurality of gas streams having desired gas compositions and flow rates according to different requirements.
Gas delivery systems are known in the field of semiconductor processing for supplying gas streams of different compositions. FIG. 1 contains a pictorial representation of an exemplary manifold system 100 as might be used in the prior art for delivering two different gas mixtures to five wafer processing stations. System 100 comprises a gas box 102 and a gas distribution section 104. System 100 comprises manual gas valves 106, gas filters 108, on-off gas ports 110, and mass flow controllers 112, as known in the art and located in gas box 102. System 100 further comprises shared gas tube 114, shared gas tube 116, gas mixers 118, gas distribution tube 120, gas distribution tube 121, gas flow restrictors 122 and gas output tubes 124, as known in the art. System 100 further comprises a plurality of threaded joints 126 and welded joints 128 for connecting gas tubes. System 100 is operable to deliver gas through gas mixing output tubes 124 containing the gas mixture flowing through shared gas mixture tube 114, the gas mixture flowing through shared gas mixture tube 116, or a gas mixture containing combined gas mixtures flowing through shared gas mixture tube 114 and shared gas mixture tube 116. System 100 has, therefore, limited flexibility. FIG. 2 depicts schematically the gas flow scheme of gas (delivery) manifold system 100. FIG. 2 depicts gas box enclosure 102 and gas delivery section 104. FIG. 2 further depicts manual gas valves 106, gas filters 108, gas ports 110, and mass flow controllers 112. FIG. 2 further depicts shared gas mixture tube 114, shared gas mixture tube 116, gas delivery tube 120, gas delivery tube 121, gas flow restrictors 122 and gas mixing output tubes 124, as known in the art. System 100 further comprises a plurality of threaded joints and welded joints for connecting gas tubes.
FIG. 3 depicts schematically the gas flow scheme of an exemplary manifold system 200 as used in the prior art for supplying different mixtures of gases to a plurality of wafer processing stations. As depicted in FIG. 3, manifold system 200 comprises a gas box 202 as known in the art and a gas delivery section 204. System 200 further comprises manual gas valves 206, gas filters 208, on-off gas ports 210, and mass flow meters 212, as known in the art and located in gas box 202. System 200 further comprises gas input tubes 220 and splittable gas input tubes 222, 223. System 200 further comprises shared gas mixture delivery tube 230, gas delivery tubes 231, on-off valves 232, mass flow meters 234 and gas output tubes 236, as known in the art and located in gas delivery section 204. Through selective use of on-off valves 210 in gas input tubes 220 and on-off valves 211 in splittable gas input tubes 222, 223, together with on-off valves 232 in gas mixture delivery tube 230 and gas delivery tubes 231, system 200 is operable to provide limited flexibility in the compositions of gas mixtures flowing to wafer processing stations 2-6. In system 200, the gas mixture compositions are flexible in the sense that the total flow rates of H2 and N2 to a particular station can be selected to be a first flow rate, a second flow rate, a third flow rate or zero flow rate. Similarly, the flow rate of CF4 to a particular station can be selected to be a first flow rate, a second flow rate or zero. The flow rates of O2, N2, CO2 and Ar, however, are limited to either one flow rate or zero. FIG. 4 contains a pictorial view 240 of gas manifold system 200 as practiced in the prior art. Pictorial view 240 shows gas box section 202 and gas delivery section 204. View 240 further shows on-off gas ports 210, 211 and mass flow meters 212, as known in the art and located in gas box 202. View 240 further shows gas input tubes 220. View 240 further shows shared gas mixture delivery tube 230 and gas delivery tubes 231, on-off valves 232, mass flow restrictors 233, mass flow meters 234, gas mixer 235 and gas output tubes 236. View 240 further shows numerous threaded joints 242 and welded joints 246 that connect various sections of gas tubing together.
Comparison of exemplary system 100 depicted in FIGS. 1 and 2, on the one hand, with system 200 depicted in FIGS. 3 and 4, on the other hand, indicates the large increase in system complexity and expense caused by the extra but limited flexibility of system 200 compared with system 100. The design of a system 200 is considerably more complicated and time-consuming and, therefore, more expensive than the design of a system 100. The extra expense of additional mass flow controllers, gas valves, and threaded and welded joints for more tube connections adds considerable expense as systems become more complex. Since the gas flows and pressure drops across valves, tube connections and angled (e.g. 90°) tube joints are difficult to model and to calculate, the actual performance of the systems becomes less predictable as complexity increases, especially for systems in which gas flow rates vary from one use application to another. In some environments, tube connections and joints cause and collect solid deposits. As systems become larger and more complex, cleaning the systems becomes more difficult, expensive and time-consuming. As systems become larger and more complex, the residence times of gases in a system increase correspondingly (with a simultaneous decrease in conductance). Also, the occurrence of so-called “dead spaces” increases with system complexity. As residence times of gases increase, the time for a gas delivery system to reach steady-state required for wafer processing also increases, leading to an overall decrease in wafer throughput. This is especially true when a gas in a gas mixture has a very low concentration compared to other gases, for example, a volumetric concentration of 0.5% of the total volumetric flow rate. A related problem of complex manifolds is the decrease in the efficiency of mixing several gases in several gas streams so that the desired compositions are delivered to wafer processing stations. Additionally, as the number of tubes, tube connections, and valves increases, the difficulty of system purging increases. Dead spaces and purging difficulty can lead to the formation of particles which can cause defects on the work piece.
Despite increased design costs and time, increased capital costs, and increasing problems regarding technical performance of gas manifold systems that provide increased gas delivery flexibility, the demand and need for such systems has increased over the years. For example, semiconductor process and product development facilities are constantly trying different gas mixtures to improve performance of semiconductor processing methods and equipment. Also, as in research and development fabrication facilities, so-called “boutique” semiconductor fabrication facilities require flexibility of gas compositions in order to use the same semiconductor processing tool for various semiconductor fabrication jobs. A common problem in the prior art is that a gas delivery system designed for a particular set of requirements is unsuitable for providing gas streams under different requirements of composition and flow rate.
Thus, there is a need in the field of semiconductor wafer processing for gas manifold systems that are economically and technically viable and that are able to deliver a plurality of gas streams having different gas mixtures to one or more wafer processing stations simultaneously and sequentially according to a variety of process requirements.